1. Field of the Invention
The present invention relates to a multi-layer electronic part built-in board, and more specifically to a multi-layer electronic part built-in board that includes alternately layered conductive and insulating layers and is mounted with built-in electronic parts.
2. Description of Background Art
Electronic control devices used in daily life, such as in vehicles and in home electric appliances are becoming increasingly sophisticated. While the scope of the circuitry included in the typical electronic control apparatus is expanding, there is a concurrent and increasing need for miniaturizing the device or apparatus itself including making the apparatus or device thinner. Accordingly, special attention is paid to the multilayer board as a circuit board suitable for satisfying the expanding needs for use in the electronic control apparatus. The multi-layer board can have surface layers and one or more internal layers that form wring layers and can contain built-in electronic parts. Since electronic parts are built into the board, the area required for mounting electronic parts on the surface can be reduced, which is advantageous for miniaturization.
In accordance with, for example, Japanese Patent Unexamined Publication No. 2005-243850, a multi-layer printed circuit board includes built-in electronic parts. A first wiring pattern is formed on the surface. The multi-layer printed circuit board has a core material where a non through hole is formed. An electronic part is embedded and fixed in the non through hole of the core material. An inter-layer insulating layer is then provided for both sides of the core material so as to embed the electronic part and the first wiring pattern. A second wiring pattern is connected to an electronic part electrode and is formed on the inter-layer insulating layer. Since the electronic part is placed in the non through hole of the core material, the multilayer printed circuit board can be miniaturized and thinned.
As will be described in detail hereinafter, it is virtually impossible to change a built-in electronic part once it is contained in the multi-layer board. As a result, the multi-layer board lacks versatility since, for example, it cannot be connected to different external circuits.
As shown in connection with the conventional configuration illustrated in FIG. 11A and FIG. 11B, it is assumed that a multi-layer electronic part built-in board 20 is supplied with detection signals from three different sensors such as first sensor 1 through third sensor 3, as external circuits and processes the signals. The first sensor 1 through the third sensor 3 are connected to lands on the surface of the multi-layer board 20 through a connector 4 provided for the multi-layer board 20. The lands are connected to a wiring pattern 8a on a top layer, a wiring pattern 8b on an internal layer, and a wiring pattern 8c on a bottom layer.
The multi-layer board 20 is configured as a layered body 5. The layered body 5 includes a glass epoxy resin as an insulator, for example, and an alternate layer of the wiring patterns 8a, 8b, and 8c where a copper foil is patterned as a conductive layer. The top layer and the bottom layer of the layered body 5 are provided with resist films 6 and 7, respectively. The resist films 6 and 7 protect and insulate the wiring patterns 8a and 8c formed on the top layer and the bottom layer.
The top and bottom layers of the multi-layer board 20 are mounted with electronic parts 10a through 10c and 12a through 12c. The internal layer of the multi-layer board 20 contains electronic parts 11a through 11c. 
The electronic parts 10a through 10c, 11a through 11c, and 12a through 12c filter, amplify, or analog-to-digital convert signals supplied from the first sensor 1 through the third sensor 3. The microcomputer may perform a specified operation based on the sensor signals.
Of the electronic parts 10a through 10c, 11a through 11c, and 12a through 12c, the electronic parts 11a through 11c are connected to the second sensor 2 and are contained in the internal layer of the multi-layer board 20 as shown in FIG. 11A and FIG. 11B. The electronic parts 11a through 11c cannot be changed virtually.
The same multi-layer board 20 cannot be used for the second sensor 2 that may feature different characteristics such as responsiveness and detection sensitivity. The multi-layer board 20 becomes less versatile.